A knee joint prosthesis typically comprises a femoral component and a tibial component. The femoral component and tibial component are designed to be surgically attached to the distal end of the femur and the proximal end of the tibia respectively. The femoral component is further designed to cooperate with the tibial component in simulating the articulating motion of an anatomical knee joint. Knee joint prostheses, in combination with ligaments and muscles, attempt to duplicate natural knee motion as well as absorb and control forces generated during the range of motion.
A typical tibial component is secured to the tibia with a stem that is implanted within the medullary canal. The stem connects to a tibial tray that provides a bearing surface for engagement with the femoral component. In this regard, in a normally shaped tibia, the medullary canal is typically offset from the center of the tibial articulating surfaces or the center of the tibial plateau. The tibial tray will be centered on a resected tibial plateau and includes an anterior edge and a posterior edge that are generally required to be of a differing shape. In order to provide a modular tibial component that is interchangeable between a right knee and a left knee, the tibial tray is typically provided with a central aperture for connection to an offset stem. The stems of prior tibial implants are required to be of differing lengths and diameters to accommodate the differing sizes of tibias while providing optimal strength and bone engagement. While these known knee joint prostheses may be effective in replacing the anatomical knee joint, they require that a multitude of stems be available for replacement surgery.
To a more limited extent, it is also known to provide a knee joint prosthesis with a fixed offset adapter for the tibia stem. The required variation of stem sizes and adapter sizes reduces the number components that must be available to perform the replacement surgery. These adapters typically have a fixed offset direction with respect to the stem and require multiple connections be made during the surgical procedure. While knee joint prosthesis with offset tibial stem adapters may provide certain identified advantages, they nevertheless can be the subject of certain improvement. What is needed is an apparatus for providing an offset for a modular tibial component that requires fewer stems, adapters and fasteners than the prior art, while allowing the offset in any direction relative the stem.